A pyrimidine 5'-deoxyribonucleoside that is 5-fluorouridine in which the hydroxy group at the 5' position is replaced by a hydrogen. It is an oral prodrug of the antineoplastic agent 5-fluorouracil. Designed to circumvent the rapid degradation of 5-fluorouracil by dihydropyrimidine dehydrogenase in the gut wall, it is converted into 5-fluorouracil in the presence of pyrimidine nucleoside phosphorylase.